Pellet injection is a primary method for fueling the plasma in magnetic confinement devices.For that goal the knowledges of pellet ablation and deposition profiles are critical.In the present study,the pellet fueling ...Pellet injection is a primary method for fueling the plasma in magnetic confinement devices.For that goal the knowledges of pellet ablation and deposition profiles are critical.In the present study,the pellet fueling code HPI2 was used to predict the ablation and deposition profiles of deuterium pellets injected into a typical H-mode discharge on the EAST tokamak.Pellet ablation and deposition profiles were evaluated for various pellet injection locations,with the aim at optimizing the pellet injection to obtain a deep fueling depth.In this study,we investigate the effect of the injection angle on the deposition depth of the pellet at different velocities and sizes.The ablation and deposition of the injected pellet are mainly studied at each injection position for three different injection angles:0°,45°,and 60°.The pellet injection on the high field side(HFS)can achieve a more ideal deposition depth than on the low field side(LFS).Among these angles,horizontal injection on the middle plane is relatively better on either the HFS or the LFS.When the injection location is 0.468 m below the middle plane on the HFS or 0.40 m above the middle plane of the LFS,it can achieve a similar deposition depth to the one of its corresponding side.When the pre-cooling effect is taken into account,the deposition depth is predicted to increase only slightly when the pellet is launched from the HFS.The findings of this study will serve as a reference for the update of pellet injection systems for the EAST tokamak.展开更多
A single-crystal diamond detector is fabricated to diagnose 14.1 MeV deuterium-tritium(D-T)fusion neutrons.The size of its diamond film is 4.5 mm×4.5 mm×500μm.This film is sandwiched by a flat,strip-pattern...A single-crystal diamond detector is fabricated to diagnose 14.1 MeV deuterium-tritium(D-T)fusion neutrons.The size of its diamond film is 4.5 mm×4.5 mm×500μm.This film is sandwiched by a flat,strip-patterned gold electrode.The dark current of this detector is experimentally measured to be lower than 0.1 nA under an electric field of 30 kV cm^(-1).This diamond detector is used to measure D-T fusion neutrons with a flux of about 7.5×10^(5) s^(-1)cm^(-2).The pronounced peak with a central energy of 8.28 MeV characterizing the^(12)C(n,α)~9Be reaction in the neutron energy spectrum is experimentally diagnosed,and the energy resolution is better than 1.69%,which is the best result reported so far using a diamond detector.A clear peak with a central energy of 6.52 MeV characterizing the^(12)C(n,n')3αreaction is also identified with an energy resolution of better than 7.67%.展开更多
The inverse Faraday effect(IFE),which usually refers to the phenomenon in which a quasi-static axial magnetic field is self-generated when a circularly polarized beam propagates in a plasma,has rarely been studied for...The inverse Faraday effect(IFE),which usually refers to the phenomenon in which a quasi-static axial magnetic field is self-generated when a circularly polarized beam propagates in a plasma,has rarely been studied for lasers with unconventional polarization states.In this paper,IFE is reconsidered for weakly relativistic full Poincarébeams,which can contain all possible laser polarization states.Starting from cold electron fluid equations and the conservation of generalized vorticity,a self-consistent theoretical model combining the nonlinear azimuthal current and diamagnetic current is presented.The theoretical results show that when such a laser propagates in a plasma,an azimuthally varying quasi-static axial magnetic field can be generated,which is quite different from the circularly polarized case.These results are qualitatively and quantitatively verified by three-dimensional particle-in-cell simulations.Our work extends the theoretical understanding of the IFE and provides a new degree of freedom in the design of magnetized plasma devices.展开更多
Dielectric laser accelerators(DLAs)are considered promising candidates for on-chip particle accelerators that can achieve high acceleration gradients.This study explores various combinations of dielectric materials an...Dielectric laser accelerators(DLAs)are considered promising candidates for on-chip particle accelerators that can achieve high acceleration gradients.This study explores various combinations of dielectric materials and accelerated structures based on the inverse Cherenkov effect.The designs utilize conventional processing methods and laser parameters currently in use.We optimize the structural model to enhance the gradient of acceleration and the electron energy gain.To achieve higher acceleration gradients and energy gains,the selection of materials and structures should be based on the initial electron energy.Furthermore,we observed that the variation of the acceleration gradient of the material is different at different initial electron energies.These findings suggest that on-chip accelerators are feasible with the help of these structures and materials.展开更多
The evolution of ablative Rayleigh–Taylor instability(ARTI)induced by single-mode stationary and time-varying perturbations in heat flux is studied numerically in two dimensions.Compared with the stationary case,time...The evolution of ablative Rayleigh–Taylor instability(ARTI)induced by single-mode stationary and time-varying perturbations in heat flux is studied numerically in two dimensions.Compared with the stationary case,time-varying heat-flux perturbation mitigates ARTI growth because of the enhanced thermal smoothing induced by the wave-like traveling heat flux.A resonance is found to form when the phase velocity of the heat-flux perturbation matches the average sound speed in the ablation region.In the resonant regime,the coherent density and temperature fluctuations enhance the electron thermal conduction in the ablation region and lead to larger ablation pressure and effective acceleration,which consequently yield higher linear growth rate and saturated bubble velocity.The enhanced effective acceleration offers increased implosion velocity but can also compromise the integrity of inertial confinement fusion shells by causing faster ARTI growth.展开更多
In addition to the magnetic confinement fusion plasma,Thomson scattering has been applied to measure electron density and temperature of low-temperature plasmas.Based on a linear magnetized plasma device,a set of Thom...In addition to the magnetic confinement fusion plasma,Thomson scattering has been applied to measure electron density and temperature of low-temperature plasmas.Based on a linear magnetized plasma device,a set of Thomson scattering diagnostic system is designed to diagnose the plasma with n_(e)=10^(18)–10^(19)m^(-3)and T_(e)=2–5eV.Due to low plasma temperature and density,this diagnostic system needs high spectral resolution and collection efficiency to meet the requirements of electron velocity distribution function measurements.Through the bench test,it is confirmed that the spectral resolution reaches 0.01 nm,and theoretical collection efficiency is high enough to obtain a Thomson scattering spectrum by 1000 accumulations.展开更多
Compact torus(CT)injection is one of the most promising methods for the central fuelling of next-generation reactor-grade fusion devices due to its high density,high velocity,and selfcontained magnetised structure.A n...Compact torus(CT)injection is one of the most promising methods for the central fuelling of next-generation reactor-grade fusion devices due to its high density,high velocity,and selfcontained magnetised structure.A newly compact torus injector(CTI)device in Keda Torus e Xperiment(KTX),named KTX-CTI,was successfully developed and tested at the University of Science and Technology in China.In this study,first,we briefly introduce the basic principles and structure of KTX-CTI,and then,present an accurate circuit model that relies on nonlinear regression analysis(NRA)for studying the current waveform of the formation region.The current waveform,displacement,and velocity of CT plasma in the acceleration region are calculated using this NRA-based one-dimensional point model.The model results were in good agreement with the experiments.The next-step upgrading reference scheme of the KTX-CTI device is preliminarily investigated using this NRA-based point model.This research can provide insights for the development of experiments and future upgrades of the device.展开更多
This research applies experimental measurements and NUBEAM,ONETWO and TRANSP modules to investigate the shine-through(ST)loss ratio and beam heating percentage of neutral beam injection on EAST.Measurements and simula...This research applies experimental measurements and NUBEAM,ONETWO and TRANSP modules to investigate the shine-through(ST)loss ratio and beam heating percentage of neutral beam injection on EAST.Measurements and simulations confirm that the ST loss ratio increases linearly with beam energy,and decreases exponentially with plasma density.Moreover,using the multi-step fitting method,we present analytical quantitative expressions of ST loss ratio and beam heating percentage,which are valuable for the high parameter long-pulse experiments of EAST.展开更多
We present particle-in-cell(PIC)simulations of laser plasma instabilities(LPIs)with a laser pulse duration of a few picoseconds.The simulation parameters are appropriate to the planar-target LPI experimental condition...We present particle-in-cell(PIC)simulations of laser plasma instabilities(LPIs)with a laser pulse duration of a few picoseconds.The simulation parameters are appropriate to the planar-target LPI experimental conditions on SG-II.In this regime,the plasmas are characterized by a long electron density scale length and a large electron density range.It is found that when the incident laser intensity is well above its backward stimulated Raman scattering(backward SRS,BSRS)threshold,the backscattered light via the primary BSRS is intense enough to excite secondary SRS(Re-SRS)in the region below one-ninth of the critical density of the incident laser.The daughter light wave via the secondary BSRS(Re-BSRS)is amplified as it propagates toward the higher-density region in the bath of broadband light generated through the primary BSRS process.A higher intensity of the incident laser not only increases the amplitude of the BSRS light but also increases the convective amplification lengths of the Re-BSRS modes by broadening the spectrum of the BSRS light.Convective amplification of Re-BSRS causes pump depletion of the primary BSRS light and may lead to an underestimate of the primary BSRS level in SP-LPI experiments.Asignificant fraction of the generation of energetic electrons is strongly correlated with the Re-BSRS modes and should be considered as a significant energy loss.展开更多
A high-frequency magnetic probe is designed and developed on the XuanL ong-50(EXL-50)spherical torus to measure high-frequency magnetic field fluctuation.The magnetic loop,radio filters,radio-frequency limiter,and dat...A high-frequency magnetic probe is designed and developed on the XuanL ong-50(EXL-50)spherical torus to measure high-frequency magnetic field fluctuation.The magnetic loop,radio filters,radio-frequency limiter,and data acquisition system of the probe are comprehensively examined.The fluctuation data from the EXL-50 plasma are analyzed in the time–frequency domain using fast Fourier transforms.Moreover,distinct high-frequency instabilities are detected using this diagnostic system.In particular,significant frequency chirping is observed,which is consistent with the bumpon-tail drive instability predicted using the Berk–Breizman model.展开更多
Interpreting experimental diagnostics data in tokamaks,while considering non-ideal effects,is challenging due to the complexity of plasmas.To address this challenge,a general synthetic diagnostics(GSD)platform has bee...Interpreting experimental diagnostics data in tokamaks,while considering non-ideal effects,is challenging due to the complexity of plasmas.To address this challenge,a general synthetic diagnostics(GSD)platform has been established that facilitates microwave imaging reflectometry and electron cyclotron emission imaging.This platform utilizes plasma profiles as input and incorporates the finite-difference time domain,ray tracing and the radiative transfer equation to calculate the propagation of plasma spontaneous radiation and the external electromagnetic field in plasmas.Benchmark tests for classical cases have been conducted to verify the accuracy of every core module in the GSD platform.Finally,2D imaging of a typical electron temperature distribution is reproduced by this platform and the results are consistent with the given real experimental data.This platform also has the potential to be extended to 3D electromagnetic field simulations and other microwave diagnostics such as cross-polarization scattering.展开更多
We present a first on-chip positron accelerator based on dielectric laser acceleration.This innovative approach significantly reduces the physical dimensions of the positron acceleration apparatus,enhancing its feasib...We present a first on-chip positron accelerator based on dielectric laser acceleration.This innovative approach significantly reduces the physical dimensions of the positron acceleration apparatus,enhancing its feasibility for diverse applications.By utilizing a stacked acceleration structure and far-infrared laser technology,we are able to achieve a seven-stage acceleration structure that surpasses the distance and energy gain of using the previous dielectric laser acceleration methods.Additionally,we are able to compress the positron beam to an ultrafast sub-femtosecond scale during the acceleration process,compared with the traditional methods,the positron beam is compressed to a greater extent.We also demonstrate the robustness of the stacked acceleration structure through the successful acceleration of the positron beam.展开更多
A compact torus injection system,KTX-CTI,has been developed for the planned injection experiments on the Keda Torus e Xperiment(KTX)reversed field pinch(RFP)device to investigate the physics and engineering issues ass...A compact torus injection system,KTX-CTI,has been developed for the planned injection experiments on the Keda Torus e Xperiment(KTX)reversed field pinch(RFP)device to investigate the physics and engineering issues associated with interaction between a compact torus(CT)and RFP.The key interests include fueling directly into the reactor center,confinement improvement,and the injection of momentum and helicity into the RFP discharges.The CT velocity and mass have been measured using a multichannel optical fiber interferometer,and for the first time the time evolution of the CT density profile during CT propagation is obtained.The effects of discharge parameters on the number of injected particles,CT velocity and CT density have been characterized:the maximum hydrogen CT plasma mass,m,CTis 50μg,corresponding to 30%of the mass in a typical KTX plasma;the CT velocity exceeds 120 km s-1.It is observed for the first time that multiple CTs can be produced and emitted during a very short period(<100μs)in one discharge,which is significant for the future study of repetitive CT injection,even with an ultra-high frequency.展开更多
The effects of electron nonlocal heat transport (NLHT) on the two-dimensional single-mode ablative Rayleigh–Taylor instability (ARTI) upto the highly nonlinear phase are reported for the first time through numerical ...The effects of electron nonlocal heat transport (NLHT) on the two-dimensional single-mode ablative Rayleigh–Taylor instability (ARTI) upto the highly nonlinear phase are reported for the first time through numerical simulations with a multigroup diffusion model. It is found thatas well as its role in the linear stabilization of ARTI growth, NLHT can also mitigate ARTI bubble nonlinear growth after the first saturationto the classical terminal velocity, compared with what is predicted by the local Spitzer–Härm model. The key factor affecting the reductionin the linear growth rate is the enhancement of the ablation velocity Va by preheating. It is found that NLHT mitigates nonlinear bubblegrowth through a mechanism involving reduction of vorticity generation. NLHT enhances ablation near the spike tip and slows down thespike, leading to weaker vortex generation as the pump of bubble reacceleration in the nonlinear stage. NLHT more effectively reduces thenonlinear growth of shorter-wavelength ARTI modes seeded by the laser imprinting phase in direct-drive laser fusion.展开更多
For collisional merging fleld-reversed conflgurations(FRCs),it is desired to have both FRCs tuned to be approximately the same,as well as to optimize each FRC to have high temperature and high translation speed so as ...For collisional merging fleld-reversed conflgurations(FRCs),it is desired to have both FRCs tuned to be approximately the same,as well as to optimize each FRC to have high temperature and high translation speed so as to retain most of the equilibrium flux after traveling a distance to the middle plane for merging.The present study reports the experimental study of a single-translated FRC in the KMAX-FRC device with various diagnostics,including a triple probe,a bolometer,several magnetic probe arrays,and a novel 2 D internal magnetic probe array.According to the measurements conducted in the present study,a maximum toroidal magnetic fleld equal to~1/3 of the external magnetic fleld inside the FRC separatrix radius is observed,and the typical parameters of a single-translated FRC near the device’s mid-plane are ne~(2–4)×10^(19)m^(-3),T_(e)~8e V,T_(i)~5 e V,r_(s)~0.2 m,l_(s)~0.6 m andφ_(()p(RR))~0.2 m Wb.The 2 D magnetic topology measurement revealed,for the flrst time,the time evolution of the overall internal magnetic flelds of a single-translated FRC,and an optimized operation regime is given in the paper.展开更多
Particle accelerators are indispensable tools in both science and industry.However,the size and cost of conventional RF accelerators limits the utility and scope of this technology.Recent research has shown that a die...Particle accelerators are indispensable tools in both science and industry.However,the size and cost of conventional RF accelerators limits the utility and scope of this technology.Recent research has shown that a dielectric laser accelerator(DLA)made of dielectric structures and driven at optical frequencies can generate particle beams with energies ranging from MeV to GeV at the tabletop level.To design DLA structures with a high acceleration gradient,we demonstrate topology optimization,which is a method used to optimize the material distribution in a specific area based on given load conditions,constraints,and performance indicators.To demonstrate the effectiveness of this approach,we propose two schemes and design several acceleration structures based on them.The optimization results demonstrate that the proposed method can be applied to structure optimization for on-chip integrated laser accelerators,producing manufacturable structures with significantly improved performance compared with previous size or shape optimization methods.These results provide new physical approaches to explore ultrafast dynamics in matter,with important implications for future laser particle accelerators based on photonic chips.展开更多
In inertial confinement fusion(ICF),polycrystalline diamond-referred to as high density carbon(HDC)-has become a promising ablator candidate.However,with smaller grain size and lower initial density,the equation of st...In inertial confinement fusion(ICF),polycrystalline diamond-referred to as high density carbon(HDC)-has become a promising ablator candidate.However,with smaller grain size and lower initial density,the equation of state(EOS)for HDC can deviate from that for single-crystal diamond,which could be a concern for ICF designs,but current experimental EOS studies for HDC are far from sufficient to clarify how initial density affects target compressibility.Presented here are measurements of the Hugoniot for HDC with an initial density of 3.23 g/cm^(3) at pressures of 17–26 Mbar.Combined with experimental data reported for nanocrystalline diamond(NCD),a stiffer compressibility of NCD due to lower initial density is confirmed.Two porous models are used for comparison and seem to offer better agreement compared with SESAME databases.Also,the effect of temperature on the Gruneisen parameter,which is usually neglected,might need to be considered for NCD under these conditions.The present data offer important support for EOS studies relevant to ICF and constrain the construction of wide-range EOS.展开更多
In the presence of energetic particles(EPs),the long-lived mode(LLM) frequency multiplication with n=1,2,3,or higher is often observed on HL-2A,where n is the toroidal mode number.Hybrid kinetic-MHD model simulations ...In the presence of energetic particles(EPs),the long-lived mode(LLM) frequency multiplication with n=1,2,3,or higher is often observed on HL-2A,where n is the toroidal mode number.Hybrid kinetic-MHD model simulations of the energetic particle(EP) driven kink/fishbone modes on a static HL-2A-like tokamak using NIMROD code find that when the background plasma pressure is relatively high,and the EP pressure and the beam energy are relatively low,the mode frequency increases almost linearly with EP pressure,and the frequency is proportional to n(’frequency multiplication’),even in the absence of any equilibrium plasma rotation.In addition,the frequency multiplication persists as the safety factor at the magnetic axis q_(0)varies.In the absence of EPs,the growth rate of the 1/1 mode is the largest;however,as the EP pressure increases,the growth rate of 2/2 modes or 3/3 modes becomes dominant,suggesting that higher-n modes are more vulnerable to EPs.These results may shed light on the understanding of the toroidal mode number dependence of kink/fishbone modes in the advanced scenarios of tokamaks with weak or reversed central magnetic shear.展开更多
In this study,NIMROD simulations are performed to investigate the effects of massive helium gas injection level on the induced disruption on EAST tokamak.It is demonstrated in simulations that two different scenarios ...In this study,NIMROD simulations are performed to investigate the effects of massive helium gas injection level on the induced disruption on EAST tokamak.It is demonstrated in simulations that two different scenarios of plasma cooling(complete cooling and partial cooling)take place for different amounts of injected impurities.For the impurity injection above a critical level,a single MHD activity is able to induce a complete core temperature collapse.For impurity injection below the critical level,a series of multiple minor disruptions occur before the complete thermal quench.展开更多
Electron sheaths have previously only been measured near a positively biased small electrode, in which a potential dip was often observed. In this paper, we present an experimental study on the electron sheath near a ...Electron sheaths have previously only been measured near a positively biased small electrode, in which a potential dip was often observed. In this paper, we present an experimental study on the electron sheath near a stainless steel plate in the presence of a weak electron beam. It is shown that the electron beam, though its density is much lower than that of the background plasma, will substantially alter the sheath structure, i.e., it causes the disappearance of the potential dip when the beam energy just exceeds the ionization potential of the neutral gas but later enhances the dip for higher energies. It is also shown that proper biases on the plate and chamber wall are the key to the formation of the electron sheath and the dip. For a fixed plate bias but with different electron beam energy, the measured thickness of the ion-free Child–Langmuir sheath agrees well with that of the theoretical model.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos.12205196 and 12275040)the National Key Research and Development Program of China (Grant No.2022YFE03090003)。
文摘Pellet injection is a primary method for fueling the plasma in magnetic confinement devices.For that goal the knowledges of pellet ablation and deposition profiles are critical.In the present study,the pellet fueling code HPI2 was used to predict the ablation and deposition profiles of deuterium pellets injected into a typical H-mode discharge on the EAST tokamak.Pellet ablation and deposition profiles were evaluated for various pellet injection locations,with the aim at optimizing the pellet injection to obtain a deep fueling depth.In this study,we investigate the effect of the injection angle on the deposition depth of the pellet at different velocities and sizes.The ablation and deposition of the injected pellet are mainly studied at each injection position for three different injection angles:0°,45°,and 60°.The pellet injection on the high field side(HFS)can achieve a more ideal deposition depth than on the low field side(LFS).Among these angles,horizontal injection on the middle plane is relatively better on either the HFS or the LFS.When the injection location is 0.468 m below the middle plane on the HFS or 0.40 m above the middle plane of the LFS,it can achieve a similar deposition depth to the one of its corresponding side.When the pre-cooling effect is taken into account,the deposition depth is predicted to increase only slightly when the pellet is launched from the HFS.The findings of this study will serve as a reference for the update of pellet injection systems for the EAST tokamak.
基金supported by National Natural Science Foundation of China(No.12075241)。
文摘A single-crystal diamond detector is fabricated to diagnose 14.1 MeV deuterium-tritium(D-T)fusion neutrons.The size of its diamond film is 4.5 mm×4.5 mm×500μm.This film is sandwiched by a flat,strip-patterned gold electrode.The dark current of this detector is experimentally measured to be lower than 0.1 nA under an electric field of 30 kV cm^(-1).This diamond detector is used to measure D-T fusion neutrons with a flux of about 7.5×10^(5) s^(-1)cm^(-2).The pronounced peak with a central energy of 8.28 MeV characterizing the^(12)C(n,α)~9Be reaction in the neutron energy spectrum is experimentally diagnosed,and the energy resolution is better than 1.69%,which is the best result reported so far using a diamond detector.A clear peak with a central energy of 6.52 MeV characterizing the^(12)C(n,n')3αreaction is also identified with an energy resolution of better than 7.67%.
基金supported by the National Natural Science Foundation of China(NSFC)under Grant No.11975014the Strategic Priority Research Program of Chinese Academy of Sciences under Grant Nos.XDA25050400 and XDA25010200.
文摘The inverse Faraday effect(IFE),which usually refers to the phenomenon in which a quasi-static axial magnetic field is self-generated when a circularly polarized beam propagates in a plasma,has rarely been studied for lasers with unconventional polarization states.In this paper,IFE is reconsidered for weakly relativistic full Poincarébeams,which can contain all possible laser polarization states.Starting from cold electron fluid equations and the conservation of generalized vorticity,a self-consistent theoretical model combining the nonlinear azimuthal current and diamagnetic current is presented.The theoretical results show that when such a laser propagates in a plasma,an azimuthally varying quasi-static axial magnetic field can be generated,which is quite different from the circularly polarized case.These results are qualitatively and quantitatively verified by three-dimensional particle-in-cell simulations.Our work extends the theoretical understanding of the IFE and provides a new degree of freedom in the design of magnetized plasma devices.
基金the National Natural Science Foundation of China(Grant No.11975214)。
文摘Dielectric laser accelerators(DLAs)are considered promising candidates for on-chip particle accelerators that can achieve high acceleration gradients.This study explores various combinations of dielectric materials and accelerated structures based on the inverse Cherenkov effect.The designs utilize conventional processing methods and laser parameters currently in use.We optimize the structural model to enhance the gradient of acceleration and the electron energy gain.To achieve higher acceleration gradients and energy gains,the selection of materials and structures should be based on the initial electron energy.Furthermore,we observed that the variation of the acceleration gradient of the material is different at different initial electron energies.These findings suggest that on-chip accelerators are feasible with the help of these structures and materials.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDA25050400 and XDA25010200)the National Natural Science Foundation of China(Grant No.12175229 and 12388101)+1 种基金the Frontier Scientific Research Program of the Deep Space Exploration Laboratory(Grant No.2022-QYKYJH-HXYF-019)by the Fundamental Research Funds for the Central Universities.
文摘The evolution of ablative Rayleigh–Taylor instability(ARTI)induced by single-mode stationary and time-varying perturbations in heat flux is studied numerically in two dimensions.Compared with the stationary case,time-varying heat-flux perturbation mitigates ARTI growth because of the enhanced thermal smoothing induced by the wave-like traveling heat flux.A resonance is found to form when the phase velocity of the heat-flux perturbation matches the average sound speed in the ablation region.In the resonant regime,the coherent density and temperature fluctuations enhance the electron thermal conduction in the ablation region and lead to larger ablation pressure and effective acceleration,which consequently yield higher linear growth rate and saturated bubble velocity.The enhanced effective acceleration offers increased implosion velocity but can also compromise the integrity of inertial confinement fusion shells by causing faster ARTI growth.
文摘In addition to the magnetic confinement fusion plasma,Thomson scattering has been applied to measure electron density and temperature of low-temperature plasmas.Based on a linear magnetized plasma device,a set of Thomson scattering diagnostic system is designed to diagnose the plasma with n_(e)=10^(18)–10^(19)m^(-3)and T_(e)=2–5eV.Due to low plasma temperature and density,this diagnostic system needs high spectral resolution and collection efficiency to meet the requirements of electron velocity distribution function measurements.Through the bench test,it is confirmed that the spectral resolution reaches 0.01 nm,and theoretical collection efficiency is high enough to obtain a Thomson scattering spectrum by 1000 accumulations.
基金supported by the National Key Research and Development Program of China(Nos.2017YFE0300500,2017YFE0300501)the Institute of Energy,Hefei Comprehensive National Science Center(Nos.19KZS205 and 21KZS202)+3 种基金the International Partnership Program of Chinese Academy of Sciences(No.Y16YZ17271)National Natural Science Foundation of China(Nos.11905143 and 12105088)Users with Excellence Program of Hefei Science Center CAS(No.2020HSC-UE008)The University Synergy Innovation Program of Anhui Province(Nos.GXXT-2021-014,GXXT2021-029)。
文摘Compact torus(CT)injection is one of the most promising methods for the central fuelling of next-generation reactor-grade fusion devices due to its high density,high velocity,and selfcontained magnetised structure.A newly compact torus injector(CTI)device in Keda Torus e Xperiment(KTX),named KTX-CTI,was successfully developed and tested at the University of Science and Technology in China.In this study,first,we briefly introduce the basic principles and structure of KTX-CTI,and then,present an accurate circuit model that relies on nonlinear regression analysis(NRA)for studying the current waveform of the formation region.The current waveform,displacement,and velocity of CT plasma in the acceleration region are calculated using this NRA-based one-dimensional point model.The model results were in good agreement with the experiments.The next-step upgrading reference scheme of the KTX-CTI device is preliminarily investigated using this NRA-based point model.This research can provide insights for the development of experiments and future upgrades of the device.
基金Supported by the Collaborative Innovation Program of Hefei Science Center,CAS (Grant No.2019HSC-CIP015)the National Natural Science Foundation of China (Grant Nos.11875290,1170529,11875253,and 11975276)+2 种基金the Fundamental Research Funds for the Central Universities (Grant No.WK3420000004)the Anhui Provincial Natural Science Foundation (Grant No.2008085J04)the National Key Research and Development Program of China (Grant No.2019YFE03020004)。
文摘This research applies experimental measurements and NUBEAM,ONETWO and TRANSP modules to investigate the shine-through(ST)loss ratio and beam heating percentage of neutral beam injection on EAST.Measurements and simulations confirm that the ST loss ratio increases linearly with beam energy,and decreases exponentially with plasma density.Moreover,using the multi-step fitting method,we present analytical quantitative expressions of ST loss ratio and beam heating percentage,which are valuable for the high parameter long-pulse experiments of EAST.
基金We thank the UCLA-IST OSIRIS Consortium for the use of OSIRIS.This research was supported by Science Challenge Project No.TZ2016005,by the Strategic Priority Research Program of the Chinese Academy of Sciences,Grant Nos.XDA25050400 and XDB16000000the National Natural Science Foundation of China(NSFC)under Grant Nos.11772324 and 11621202the Fundamental Research Funds for the Central Universities.Some of the numerical calculations in this paper were done on the supercomputing system at the Supercomputing Center of the University of Science and Technology of China.
文摘We present particle-in-cell(PIC)simulations of laser plasma instabilities(LPIs)with a laser pulse duration of a few picoseconds.The simulation parameters are appropriate to the planar-target LPI experimental conditions on SG-II.In this regime,the plasmas are characterized by a long electron density scale length and a large electron density range.It is found that when the incident laser intensity is well above its backward stimulated Raman scattering(backward SRS,BSRS)threshold,the backscattered light via the primary BSRS is intense enough to excite secondary SRS(Re-SRS)in the region below one-ninth of the critical density of the incident laser.The daughter light wave via the secondary BSRS(Re-BSRS)is amplified as it propagates toward the higher-density region in the bath of broadband light generated through the primary BSRS process.A higher intensity of the incident laser not only increases the amplitude of the BSRS light but also increases the convective amplification lengths of the Re-BSRS modes by broadening the spectrum of the BSRS light.Convective amplification of Re-BSRS causes pump depletion of the primary BSRS light and may lead to an underestimate of the primary BSRS level in SP-LPI experiments.Asignificant fraction of the generation of energetic electrons is strongly correlated with the Re-BSRS modes and should be considered as a significant energy loss.
基金supported by National Natural Science Foundation of China(No.11706151)。
文摘A high-frequency magnetic probe is designed and developed on the XuanL ong-50(EXL-50)spherical torus to measure high-frequency magnetic field fluctuation.The magnetic loop,radio filters,radio-frequency limiter,and data acquisition system of the probe are comprehensively examined.The fluctuation data from the EXL-50 plasma are analyzed in the time–frequency domain using fast Fourier transforms.Moreover,distinct high-frequency instabilities are detected using this diagnostic system.In particular,significant frequency chirping is observed,which is consistent with the bumpon-tail drive instability predicted using the Berk–Breizman model.
基金supported by the National Magnetic Confinement Fusion Energy Program of China(No.2019YFE03020001)the Collaborative Innovation Program of Hefei Science Center,CAS(No.2021HSC-CIP010)the Fundamental Research Funds for the Central Universities。
文摘Interpreting experimental diagnostics data in tokamaks,while considering non-ideal effects,is challenging due to the complexity of plasmas.To address this challenge,a general synthetic diagnostics(GSD)platform has been established that facilitates microwave imaging reflectometry and electron cyclotron emission imaging.This platform utilizes plasma profiles as input and incorporates the finite-difference time domain,ray tracing and the radiative transfer equation to calculate the propagation of plasma spontaneous radiation and the external electromagnetic field in plasmas.Benchmark tests for classical cases have been conducted to verify the accuracy of every core module in the GSD platform.Finally,2D imaging of a typical electron temperature distribution is reproduced by this platform and the results are consistent with the given real experimental data.This platform also has the potential to be extended to 3D electromagnetic field simulations and other microwave diagnostics such as cross-polarization scattering.
基金supported by the National Natural Science Foundation of China(Grant No.11975214).
文摘We present a first on-chip positron accelerator based on dielectric laser acceleration.This innovative approach significantly reduces the physical dimensions of the positron acceleration apparatus,enhancing its feasibility for diverse applications.By utilizing a stacked acceleration structure and far-infrared laser technology,we are able to achieve a seven-stage acceleration structure that surpasses the distance and energy gain of using the previous dielectric laser acceleration methods.Additionally,we are able to compress the positron beam to an ultrafast sub-femtosecond scale during the acceleration process,compared with the traditional methods,the positron beam is compressed to a greater extent.We also demonstrate the robustness of the stacked acceleration structure through the successful acceleration of the positron beam.
基金supported by the National Magnetic Confinement Fusion Science Program of China(Nos.2017YFE0301700 and 2017YFE0301701)National Natural Science Foundation of China(Nos.11875255,11635008,11375188 and 11975231)。
文摘A compact torus injection system,KTX-CTI,has been developed for the planned injection experiments on the Keda Torus e Xperiment(KTX)reversed field pinch(RFP)device to investigate the physics and engineering issues associated with interaction between a compact torus(CT)and RFP.The key interests include fueling directly into the reactor center,confinement improvement,and the injection of momentum and helicity into the RFP discharges.The CT velocity and mass have been measured using a multichannel optical fiber interferometer,and for the first time the time evolution of the CT density profile during CT propagation is obtained.The effects of discharge parameters on the number of injected particles,CT velocity and CT density have been characterized:the maximum hydrogen CT plasma mass,m,CTis 50μg,corresponding to 30%of the mass in a typical KTX plasma;the CT velocity exceeds 120 km s-1.It is observed for the first time that multiple CTs can be produced and emitted during a very short period(<100μs)in one discharge,which is significant for the future study of repetitive CT injection,even with an ultra-high frequency.
基金This research was supported by Science Challenge Project No.TZ2016001by the Strategic Priority Research Program of Chinese Academy of Sciences under Grant Nos.XDA25050400,XDA25010200,and XDB16000000by the National Natural Science Foundation of China(NSFC)under Grant Nos.U1530261,12175229,and 11621202,and by the Fundamental Research Funds for the Central Universities.Some of the numerical calculations in this paper were performed on the supercomputing system at the Supercomputing Center of the University of Science and Technology of China.
文摘The effects of electron nonlocal heat transport (NLHT) on the two-dimensional single-mode ablative Rayleigh–Taylor instability (ARTI) upto the highly nonlinear phase are reported for the first time through numerical simulations with a multigroup diffusion model. It is found thatas well as its role in the linear stabilization of ARTI growth, NLHT can also mitigate ARTI bubble nonlinear growth after the first saturationto the classical terminal velocity, compared with what is predicted by the local Spitzer–Härm model. The key factor affecting the reductionin the linear growth rate is the enhancement of the ablation velocity Va by preheating. It is found that NLHT mitigates nonlinear bubblegrowth through a mechanism involving reduction of vorticity generation. NLHT enhances ablation near the spike tip and slows down thespike, leading to weaker vortex generation as the pump of bubble reacceleration in the nonlinear stage. NLHT more effectively reduces thenonlinear growth of shorter-wavelength ARTI modes seeded by the laser imprinting phase in direct-drive laser fusion.
基金supported by the National Key R&D Program of China(No.2017YFE0301802)National Natural Science Foundation of China(No.12175226)。
文摘For collisional merging fleld-reversed conflgurations(FRCs),it is desired to have both FRCs tuned to be approximately the same,as well as to optimize each FRC to have high temperature and high translation speed so as to retain most of the equilibrium flux after traveling a distance to the middle plane for merging.The present study reports the experimental study of a single-translated FRC in the KMAX-FRC device with various diagnostics,including a triple probe,a bolometer,several magnetic probe arrays,and a novel 2 D internal magnetic probe array.According to the measurements conducted in the present study,a maximum toroidal magnetic fleld equal to~1/3 of the external magnetic fleld inside the FRC separatrix radius is observed,and the typical parameters of a single-translated FRC near the device’s mid-plane are ne~(2–4)×10^(19)m^(-3),T_(e)~8e V,T_(i)~5 e V,r_(s)~0.2 m,l_(s)~0.6 m andφ_(()p(RR))~0.2 m Wb.The 2 D magnetic topology measurement revealed,for the flrst time,the time evolution of the overall internal magnetic flelds of a single-translated FRC,and an optimized operation regime is given in the paper.
基金the National Natural Science Foundation of China(Nos.12004353,11975214,11991071,11905202,12174350)Key Laboratory Foundation of The Sciences and Technology on Plasma Physics Laboratory(No.6142A04200103)Independent scientific research(No.JCKYS2021212011).
文摘Particle accelerators are indispensable tools in both science and industry.However,the size and cost of conventional RF accelerators limits the utility and scope of this technology.Recent research has shown that a dielectric laser accelerator(DLA)made of dielectric structures and driven at optical frequencies can generate particle beams with energies ranging from MeV to GeV at the tabletop level.To design DLA structures with a high acceleration gradient,we demonstrate topology optimization,which is a method used to optimize the material distribution in a specific area based on given load conditions,constraints,and performance indicators.To demonstrate the effectiveness of this approach,we propose two schemes and design several acceleration structures based on them.The optimization results demonstrate that the proposed method can be applied to structure optimization for on-chip integrated laser accelerators,producing manufacturable structures with significantly improved performance compared with previous size or shape optimization methods.These results provide new physical approaches to explore ultrafast dynamics in matter,with important implications for future laser particle accelerators based on photonic chips.
基金supported by the National Key R&D Program of China(Grant No.2017YFA0403201)the Science Challenge Project(Grant No.TZ2016001)the National Natural Science Foundation of China(Grant Nos.11805183,12074351,and 11704351).
文摘In inertial confinement fusion(ICF),polycrystalline diamond-referred to as high density carbon(HDC)-has become a promising ablator candidate.However,with smaller grain size and lower initial density,the equation of state(EOS)for HDC can deviate from that for single-crystal diamond,which could be a concern for ICF designs,but current experimental EOS studies for HDC are far from sufficient to clarify how initial density affects target compressibility.Presented here are measurements of the Hugoniot for HDC with an initial density of 3.23 g/cm^(3) at pressures of 17–26 Mbar.Combined with experimental data reported for nanocrystalline diamond(NCD),a stiffer compressibility of NCD due to lower initial density is confirmed.Two porous models are used for comparison and seem to offer better agreement compared with SESAME databases.Also,the effect of temperature on the Gruneisen parameter,which is usually neglected,might need to be considered for NCD under these conditions.The present data offer important support for EOS studies relevant to ICF and constrain the construction of wide-range EOS.
基金supported by the National Magnetic Confinement Fusion Program of China (No. 2019YFE03050004)National Natural Science Foundation of China (Nos.11875253,11775221,51821005 and 11875018)+2 种基金the Fundamental Research Funds for the Central Universities (Nos.WK3420000004 and 2019kfyXJJS193)the Collaborative Innovation Program of Hefei Science Center,CAS (No. 2019HSC-CIP015)the U S Department of Energy (Nos.DEFG02-86ER53218 and DE-SC0018001)
文摘In the presence of energetic particles(EPs),the long-lived mode(LLM) frequency multiplication with n=1,2,3,or higher is often observed on HL-2A,where n is the toroidal mode number.Hybrid kinetic-MHD model simulations of the energetic particle(EP) driven kink/fishbone modes on a static HL-2A-like tokamak using NIMROD code find that when the background plasma pressure is relatively high,and the EP pressure and the beam energy are relatively low,the mode frequency increases almost linearly with EP pressure,and the frequency is proportional to n(’frequency multiplication’),even in the absence of any equilibrium plasma rotation.In addition,the frequency multiplication persists as the safety factor at the magnetic axis q_(0)varies.In the absence of EPs,the growth rate of the 1/1 mode is the largest;however,as the EP pressure increases,the growth rate of 2/2 modes or 3/3 modes becomes dominant,suggesting that higher-n modes are more vulnerable to EPs.These results may shed light on the understanding of the toroidal mode number dependence of kink/fishbone modes in the advanced scenarios of tokamaks with weak or reversed central magnetic shear.
基金supported by the National Magnetic Confinement Fusion Science Program of China(No.2019YFE03050004)National Natural Science Foundation of China(Nos.11775221 and 51821005)+1 种基金US DOE(Nos.DEFG02-86ER53218 and DESC0018001)the Fundamental Research Funds for the Central Universities at Huazhong University of Science and Technology(No.2019kfyXJJS193).
文摘In this study,NIMROD simulations are performed to investigate the effects of massive helium gas injection level on the induced disruption on EAST tokamak.It is demonstrated in simulations that two different scenarios of plasma cooling(complete cooling and partial cooling)take place for different amounts of injected impurities.For the impurity injection above a critical level,a single MHD activity is able to induce a complete core temperature collapse.For impurity injection below the critical level,a series of multiple minor disruptions occur before the complete thermal quench.
基金supported by National Natural Science Foundation of China(Nos.11975229 and 11705201)。
文摘Electron sheaths have previously only been measured near a positively biased small electrode, in which a potential dip was often observed. In this paper, we present an experimental study on the electron sheath near a stainless steel plate in the presence of a weak electron beam. It is shown that the electron beam, though its density is much lower than that of the background plasma, will substantially alter the sheath structure, i.e., it causes the disappearance of the potential dip when the beam energy just exceeds the ionization potential of the neutral gas but later enhances the dip for higher energies. It is also shown that proper biases on the plate and chamber wall are the key to the formation of the electron sheath and the dip. For a fixed plate bias but with different electron beam energy, the measured thickness of the ion-free Child–Langmuir sheath agrees well with that of the theoretical model.
